(1) Field of the Invention
This invention relates to a technique for applying adhesive tape such as protective tape to surfaces of workpieces such as semiconductor wafers, lead frames or various printed circuit boards.
(2) Description of the Related Art
Methods of planarizing semiconductor wafers (hereinafter simply called “wafers”) include mechanical methods such as grinding and polishing (CMP), and chemical methods using etching. When these methods are used to planarize the wafers, protective adhesive tape (hereinafter simply called “protective tape”) is applied to the front surfaces of the wafers to protect the wafer surfaces having circuit patterns formed thereon.
In a back-grinding apparatus, for example, the front surface (pattern surface) of a wafer loaded therein is suction-supported by a chuck table and the back surface of the wafer is ground with a grinder. At this time, the back surface of the wafer is ground, with the protective tape applied to the front surface of the wafer to avoid the pattern being damaged under the stress of grinding and to avoid contamination of the pattern.
In processing the back surface of the wafer, the protective tape may not be applied to the front surface of the wafer to have the adhesive of the protective tape filling irregularities, particularly depressions, on the front surface, and to have the surface of the tape in a substantially planar state. Then, the following problems are encountered.
The water used in time of back-surface processing infiltrates into spaces in the depressions. Further, the wafer has a greater overall thickness at elevated portions than at depressed portions. The thicker portions may be ground to be the thinner, resulting in the inconvenience of lowering the accuracy of processing thickness over the wafer surface.
In order to avoid such an inconvenience, it has been conventional practice to increase the pressure of an applicator roller for pressing the adhesive tape on the wafer surface, to heat the wafer through the chuck table and soften the adhesive, thereby facilitating filling of the depressions, or to combine these measures. In this way, an attempt has been made to apply the protective tape reliably even to the irregularities on the patterned surface.
However, both of these measures of increasing the pressure of the applicator roller and heating the wafer invariably apply the protective tape by forcibly deforming the protective tape itself. Consequently, the wafer processed to be thin could be subjected to an increased curvature under the influence of a stress stored in the protective tape forcibly deformed.
Moreover, there have been increased cases in recent years of back-surface processing of wafers, such as flip chips, having bumps formed thereon. Such wafers tend to have increased level differences on the surfaces. Thus, a desire exists for an adhesive tape applying technique capable of coping with such large level differences.